1. Field of the Invention
The present invention relates to an intermodule coupling mechanism and, in particular, to such a coupling mechanism which equalizes external and internal pressures exerted upon the coupling between electrical and similar connectors.
2. Description of the Prior Art
Coupling mechanisms of the type described are generally used in the assembly of long towed hydrophone arrays which are used, for example, in oil exploration and ship detection using acoustic means. For practical handling, fabrication and at sea sparing reasons, long towed array hydrophone arrays must be made in modular lengths which can be coupled together. It is desirable that the coupling be smooth, rigid and the same diameter as that of the flexible hose of which the modules are constructed, be of short length, light in weight, and easily manufactured. It should also have high reliability and a design which allows assembly from the outside without access to the back side of the coupling after it is installed on the module hose.
In the past, module couplings have been designed so that an air gap exists between the two halves of the coupling. This design has the advantage of allowing modules to be sealed at each end so that the "fill fluid" used to fill each module hose, comprising a light oil like hydrocarbon insulating liquid, is completely contained and so that the uncoupled module will be handled as an essentially dry unit. This simplifies assembly and disassembly of the fluid filled towed array. The electrical path between modules has normally been completed with a pigtail connector cable. This cable runs between the male and female pressure tight feedthrough connector, which penetrates the bulkhead fluid barrier located in each mechanical coupling half, and is joined in the sealed air chamber between them.
The disadvantage of this type of module end coupling design is the complexity and expense resulting from having to make two pressure-proof electrical connectors per joint. Since the array modules often operate at ocean depths of five to ten thousand feet, each electrical connector, which penetrates the "fill fluid" retaining bulkhead and reaches into the air space between the couplings, must be able to withstand a hydrostatic pressure of 2500 to 4500 psi. Such pressure is due to the fact that the rubber hose transmits the sea water hydrostatic pressure to the "fill fluid" through the flexible hose walls. On the other hand, the intercoupling air space is at atmospheric pressure, because the coupling joint was made and sealed in air above the surface of the water. The resulting pressure differential not only requires an expensive electrical connector but has been found to be the weakest link in array construction, from the point of view of reliability.
While it may be desirable to add "fill fluid" at the time of assembly to fill the intercoupling air space, complete filling is not possible. Thus, any remaining air allows a pressure differential to develop between the two sides of the electrical connector as before. Even if complete filling were possible, the low temperatures encountered in the ocean reduce the volume of the fill fluid, resulting in the same effect.
Another possibility is to separate the two rigid halves of the coupler slightly and bridge the gap with a piece of flexible hose. Now, when the space between the couplers is almost "completely" oil filled, any minor voids are unimportant because the flexible portion deflects, allowing the sea water hydrostatic pressure to be transmitted to the "fill fluid" oil between the coupling. In this situation, the fill fluid on either side of the electrical connector feedthroughs is balanced. Since no pressure differential exists, a lower cost connector can be used along with overall lighter construction of the coupling walls.
The disadvantages of this approach are that the rather large volume of "fill fluid" oil in between the connectors must be drained and refilled each time a set of modules is decoupled. Thus, the module is essentially "wet" and inconvenient to handle, particularly at sea. Also, the oil that has replaced the air does not provide light weight coupling, which is desirable, although this situation is partially offset because a lighter overall construction is now satisfactory.
In summary, towed array module mechanical/electrical connectors have been used which withstood hydrostatic pressure across the wet to dry bulkhead of up to 3000 pounds. However, experience revealed that this has induced electrical connector failures in the situation where extremely high reliability is required. Alternate pressure compensated connections using a separate piece of coupling hose have been crude and complex to mate and require separate filling.